ASTM D5338 Testing: Determining Aerobic Biodegradation of Plastic Materials Under Controlled Composting Conditions
What is ASTM D5338 Testing?
The standard test method, according to ASTM D5338, enables one to assess the aerobic biodegradation of plastic materials under composting conditions that simulate the biological activity occurring within an industrial composting process. This test measures the conversion of carbon in the plastic material to carbon dioxide (CO₂) through microbial action in an oxygen-rich environment.
This provides a quantitative measure of the degree and rate at which plastic decomposes in the presence of heat, moisture, oxygen, and microorganisms, and it assists manufacturers in determining if their materials are truly compostable.
Why is ASTM D5338 Testing Important?
As global sustainability goals push for reduced plastic waste, ASTM D5338 testing plays a vital role in validating claims related to biodegradability and compostability.
This test helps:
- Evaluate the biodegradation performance of plastics in composting environments.
- Support eco-labeling and certification (e.g., EN 13432, ISO 17088).
- Ensure compliance with environmental regulations and compostable product standards.
- Promote sustainable product development by comparing bio-based and petroleum-based materials to identify the most effective options.
ASTM D5338 is recognized globally as the benchmark test for assessing the aerobic biodegradation of plastics intended for industrial composting.
Which Materials Can Be Tested Under ASTM D5338?
This method is suitable for a variety of organic-based plastic materials, including:
- Biodegradable polymers: PLA (Polylactic Acid), PHA, PBAT, PBS
- Starch-based plastics and blends
- Compostable films and packaging materials
- Natural polymer composites
- Modified or additive-enhanced plastics designed to promote biodegradation
Materials may be tested in forms such as films, granules, powders, or molded parts, depending on their intended use.
What Information Do ASTM D5338 Test Results Provide?
The test provides a quantitative understanding of a material’s biodegradation behavior under composting conditions, summarized as follows:
| Parameter | Unit | Description |
| CO₂ Evolution | mg or % | Amount of CO₂ generated due to microbial degradation |
| Degree of Biodegradation | % | Portion of total organic carbon converted into CO₂ |
| Biodegradation Rate | % per day | The speed at which the material biodegrades |
| Lag Phase | days | Time before active biodegradation begins |
These data indicate whether a material is readily, partially, or slowly biodegradable under composting conditions.
What Industries Use ASTM D5338 Testing?
ASTM D5338 testing is widely used across industries focused on sustainability and green materials, including:
- Packaging: Compostable bags, films, trays, and food-service containers
- Consumer Goods: Biodegradable cutlery, straws, and tableware
- Agriculture: Compostable mulch films and plant pots
- Biomedical: Bio-based medical disposables and polymer films
- Research & Development: New material formulation and environmental impact studies
The data obtained from this test helps support eco-certification, product labeling, and regulatory compliance.
What Equipment Is Used for ASTM D5338 Testing?
A typical ASTM D5338 test setup includes:
- Composting reactors or respirometers with air circulation systems
- CO₂ measurement apparatus (e.g., alkali traps or infrared gas analyzers)
- Temperature-controlled incubator (maintained at 58°C ± 2°C)
- Humidity and aeration control system
- Reference materials, such as pure cellulose powder, for comparison
These components ensure controlled and reproducible composting conditions for accurate biodegradation analysis.
How Is the ASTM D5338 Test Performed?
Step-by-Step Procedure:
- Sample Preparation:
Plastic test specimens are prepared in known mass and shape (film, powder, or granules). The carbon content is determined to calculate the theoretical CO₂ yield. - Compost Inoculum Preparation:
Compost inoculum is obtained from active compost piles, which contain a mixture of organic waste materials and a diverse microbial community. - Test Setup:
Samples are mixed with the compost inoculum in controlled composting reactors. Control and reference samples (e.g., cellulose) are also prepared. - Incubation:
Reactors are maintained under aerobic conditions at 58°C ± 2°C, which replicates the industrial composting temperatures. Moisture and aeration are monitored to sustain microbial activity. - Measurement:
CO₂ evolution is measured periodically using gas collection systems or CO₂ traps. - Data Analysis:
The cumulative CO₂ production is compared to the theoretical maximum, and biodegradation is expressed as a percentage of total organic carbon converted to CO₂.
What Are the Standard Test Conditions?
| Parameter | Typical Condition |
| Temperature | 58°C ± 2°C |
| Oxygen Level | Aerobic (continuous air supply) |
| Moisture Content | 50–60% of water-holding capacity |
| Duration | Up to 180 days or until biodegradation stabilizes |
| Reference Material | Cellulose powder |
| Control | Compost without a test sample |
Maintaining these controlled conditions ensures consistency and reproducibility of test results.
Key Properties Measured
ASTM D5338 measures the extent and rate of aerobic biodegradation of plastic materials under thermophilic composting conditions. The primary property quantified is the biodegradability, expressed as the percentage of organic carbon converted to CO₂ over time.
This property helps determine whether a material will fully biodegrade within a commercial composting facility, ensuring compliance with compostability standards.
Related Testing Methods
- ASTM D6400 – Labeling of plastics designed to be aerobically composted in municipal facilities
- ASTM D5526 – Anaerobic biodegradation of plastics under landfill conditions
- ASTM D5988 – Aerobic biodegradation of plastics in soil
- ISO 14855 – Determination of ultimate aerobic biodegradability under controlled composting conditions
Together, these standards provide a comprehensive framework for evaluating plastic biodegradability under various environmental conditions.
Conclusion
ASTM D5338 provides a scientifically rigorous method for assessing the aerobic biodegradation of plastic materials under controlled composting conditions. Measuring CO₂ evolution, the test accurately reflects the conversion of organic carbon to carbon dioxide, simulating real-world composting processes.
The method is thus an essential tool for manufacturers, researchers, and regulatory organizations that intend to verify compostability by applying international standards and fostering sustainability in product design.
Ultimately, ASTM D5338 plays a critical role in the transition toward a circular economy, enabling the shift whereby plastics are designed to safely return to nature through industrial composting.
Why Choose Infinita Lab for ASTM D5338?
Infinita Lab is a leading provider of ASTM D5338 and streamlined material testing services, addressing the critical challenges faced by emerging businesses and established enterprises. With access to a vast network of over 2,000+ accredited partner labs across the United States, Infinita Lab ensures rapid, accurate, and cost-effective testing solutions. The company’s unique value proposition includes comprehensive project management, confidentiality assurance, and seamless communication through a Single Point of Contact (SPOC) model. By eliminating inefficiencies in traditional material testing workflows, Infinita Lab accelerates research and development (R&D) processes.
Looking for a trusted partner to achieve your research goals? Schedule a meeting with us, send us a request, or call us at (888) 878-3090 to learn more about our services and how we can support you.
FAQs on ASTM D5338 – Determining Aerobic Biodegradation
What is the purpose of ASTM D5338 testing? ASTM D5338 evaluates the aerobic biodegradation of plastic materials when exposed to controlled composting conditions, simulating industrial composting environments. It measures how effectively the carbon in the test material is converted into carbon dioxide (CO₂) by microorganisms, indicating its compostability and environmental performance.
What does the test measure? ASTM D5338 measures the amount of CO₂ evolved during composting, which corresponds to the extent and rate of biodegradation of the plastic material. The results are expressed as a percentage of total organic carbon converted to CO₂, indicating the extent to which the plastic decomposes under composting conditions.
What are the control and reference materials in this test? Control: Compost without any added plastic material, used to measure background CO₂ production. Reference Material: Cellulose powder, which is readily biodegradable and serves as a positive control to validate microbial activity and test reliability.
How long does the ASTM D5338 test take? The duration typically ranges from 45 to 180 days, depending on the material’s degradation behavior. The test continues until the biodegradation curve stabilizes, meaning microbial activity has significantly decreased and no additional CO₂ evolution is observed.
